Dentin is a portion of the tooth internal to the enamel and cementum that has a radially striated appearance owing to a large number of fine canals or tubules known as the dentinal tubules. These run from the pulp cavity to the periphery of the dentin and are generally one to two microns in diameter at their base and somewhat narrower at their periphery.
Hypersensitive teeth is an irritating and painful condition caused by the existence of these hollow, dentin tubules that allow the nerves within the root canal and pulp of the tooth to be influenced by the external oral environment. Whereas the dentinal tubules are normally shielded from the external environment by the tooth enamel or cementum, the condition of tooth hypersensitivity arises when the enamel or cementum has eroded or recedes in areas on the tooth, particularly along the gum line, which directly exposes the tubules. Heat, cold, chemicals and physical or mechanical pressure or stimuli such as brushing all are able to irritate the nerve through the dentin tubules and thereby create the unpleasant sensation of pain. The pain of sensitive teeth results from these stimuli which cause fluid movements in the dentinal tubules that activate pulpal nerve endings. Such pain certainly does not encourage daily oral care and treatment and so as a result those plagued with hypersensitive teeth do not brush as often as they should nor can they always enjoy the food and beverages available in today's society.
Various attempts have been made in the art to cure or treat hypersensitive teeth so as to relieve the associated pain. U.S. Pat. No. 4,057,021 to Pashley et. al. teaches the desensitization of these teeth through the application of an alkali metal salt or ammonium oxalate to the surface of the tooth. U.S. Pat. Nos. 4,631,185 and 4,751,072 to Kim disclose the desensitization of teeth using oral compositions comprising potassium salts while U.S. Pat. No. 4,990,327 to Neirinchx describes the desensitization of teeth with strontium and fluoride ions. These chemicals act directly on the nerve endings within the tooth by somehow blocking the electrochemical impulses that are fired from one nerve cell to the next in the transmission of the pain signal. Other prior art methods disclose the treatment of hypersensitive teeth using zinc and strontium ions (U.S. Pat. No. 3,888,976 to Mlksey et. al.), chloride salts (U.S. Pat. No. 3,689,686 to Svajda) and apatite particles (U.S. Pat. Nos. 4,634,589 and 4,710,372 to Scheller). Although these chemical methods of treatment provide relief to some degree, they often require several weeks of application before they are effective.
Other methods have developed over the years which utilize various polymer systems for delivery of active agents to the teeth and gums. U.S. Pat. No. 4,685,883 to Jernberg discloses the use of biodegradable microsphere to deliver chemotherapeutic agents to lesions in the gums. U.S. Pat. No. 3,956,480 to Dichter et. al. describes and claims the treatment of teeth with anionic polymers that are complexed with a cationic antimicrobial agent such as chlorhexidine.
Along a similar vein U.S. Pat. Nos. 5,300,290 and 5,320,842 to J. Spencer disclose the use of solid polymeric particles such as polystyrene, polymethyl methacrylate, and polyvinyltoluene among others that have an ionically charged outer surface onto which an oppositely charged antimicrobial agent such as chlorhexidine is absorbed. The composition is used for antimicrobial action in the oral cavity in general and is not used in the treatment of hypersensitive teeth.
Two related patents disclose the use of similar microparticles for desensitizing teeth. U.S. Pat. Nos. 5,250,288 and 5,211,939 to Turetsky et. al. disclose a dentifrice comprising positively charged polystyrene particles which, it is postulated, desensitize the tooth by clinging to the surface of the teeth and block the dentin tubules thereby protecting the nerve from exposure to outside stimuli. The particles are generally from about 0.01 to 3.0 microns and may have an antimicrobial, analgesic or other therapeutic substance absorbed therein.
Finally, U.S. Pat. No. 5,270,031 to Lim et. al. discloses oral compositions for relieving the pain and discomfort caused by hypersensitive teeth consisting of water-soluble or water-swellable polyelectrolyte salts. The polyelectrolyte salts can comprise the anionic, cationic or amphoteric forms of methyl vinylether and maleic anhydride copolymers or polyacrylic acid polymers with sodium, calcium, potassium, ammonium, zinc and other similar metals.
However, in order for any of the aforementioned compositions to be effective in reducing the pain and discomfort of hypersensitive teeth, they must be able to enter the tubule for blockage thereof or to essentially anesthetize the nerve endings in the dentin pulp area. It has been shown that the tubules of sensitive human dentin may also contain organic material that prevents the bulk movement of certain materials into the tubules. Additionally, there is evidence that there is a continuous outward flow of fluid when vital dentin is exposed and the dentinal smear layer is removed. This outward fluid flow from the tubules would certainly counteract the ability of any desensitizing materials to enter the tubules for blockage or nerve anesthesia. The mere application of these materials with a toothbrush or paste or in solution as a mouthwash would not generate the sufficient driving force to cause the desensitizing materials to enter the tubules of live sensitive dentin. Hence, the need exists for a means to better apply a desensitizing composition to the tooth surface so as to insure tubule blockage and/or nerve anesthesia.
The prior art shows a number of auxiliary applicator type devices used in the cleaning or massaging of the teeth and gums. U.S. Pat. No. 1,248,675 to Kouinsky and U.S. Pat. No. 140,492 to O'Donoghue both disclose a tooth brush with two brush members located at opposite ends of the brush handle that are perpendicular to each other. One brush member is for brushing the teeth up and down while the other brushes from side to side. U.S. Pat. No. 2,110,315 to Wolfson discloses a toothbrush with a rubber serrated fusto-conical cup at the other end. The cup is used to massage the teeth and gums with a backward-forward motion of the serrated edges. U.S. Pat. No. 2,164,219 to McGerry discloses a toothbrush with distally mounted rubber cup members attached to the body of the handle by spring metal plates which urge the cups into crevices of the teeth as the device is moved over them during cleaning.
U.S. Pat. No. 4,543,679 to Rosofsky et. al. discloses a toothbrush assembly with a brush and oral hygiene device comprised of a porous material for the dispensing of an active agent on the teeth. This can then be rubbed over the teeth and a cleaning or antibacterial agent released thereon. Finally, U.S. Pat. No. 5,205,302 to Lemon discloses a toothbrush with a soft brush gum stimulator using a soft brush consisting of high density thin fibers. The stimulator may be shaped as a tapered pintle brush comprised of elongated center fibers or may be a cup-shaped brush, both of which are removable and replaceable from the end of the handle. In both cases the oral hygiene device is comprised of brush fibers for cleaning the interstitial space between the teeth.